1. Field of the Invention
This invention relates generally to fire and explosion sensing and suppression systems, and more particularly, to such systems in which radiation is detected in at least two different spectral bands.
2. Background Art
Certain types of fire suppression systems utilize fire sensors having multiple signal processing channels which respond to fire- or explosion-produced electromagnetic radiation to generate a fire suppression command output signal. The fire suppression command output signal is used to trigger the release of a fire suppression agent, such as halon gas.
Such systems employ more than one signal processing channel in order to discriminate against radiation which is not associated with a fire or explosion requiring suppression. For example, hydrocarbon fires produce long wavelength infrared radiation in the 6 to 30 micrometer spectral band, and also short wavelength radiation in the 0.7 to 1.2 micrometer spectral band, at characteristic relative intensities. Multiple channel fire sensors have been designed which produce an output signal only when radiation is detected in each of the aforementioned spectral bands above predefined levels associated with a fire of a predetermined size, and in relative amounts associated with a hydrocarbon fire. Such systems are resistant to false triggering from, for example, direct exposure to a high intensity lamp, heater, flash light or the like. One such multiple channel fire suppression system of the above type is disclosed and claimed in U.S. Pat. No. 3,931,521, which issued to R. J. Cinzori and which is assigned to the present assignee.
While the aforementioned fire suppression systems operate satisfactorily in many environments, nonetheless certain adverse conditions may occur which interfere with the operation of one or more of the radiation channels. For example, if an area being monitored by such a fire sensor system becomes filled with smoke, while detection in the long wavelength region may be substantially unaffected, short wavelength radiation from a potentially dangerous fire may be obscured from the sensor system by the smoke.
Another, quite serious problem which can occur in the operation of multi-channel fire suppression systems is the failure to operate because of contamination on the sensor windows. For example, multi-channel fire sensor systems are used in armored personnel carriers to protect the occupants from fires which may start in the engine compartment of the vehicle. The sensors are placed physically within the engine compartment in such instances, thus affording as early as possible detection of an engine compartment fire. Such a armored carrier may be put to considerable use, and go for a considerable length of time before a fire occurs requiring the activation of the suppression system. Over such an extended period of time, the windows of the sensors of a fire suppression system located within the engine compartment are likely to become covered over with a film of contaminates including grease, sand, dust, and other components frequently found in such a location. A sufficiently thick build-up of such contaminants will prevent the effective operation of the typical multi-channel fire suppression system, primarily due to blockage of the short wavelength channel thereof.
The failure of a fire suppression system to operate properly, for example, to suppress a fire in the engine compartment of an armored personnel carrier, could be disastrous to the personnel the fire suppression system is designed to protect. There is therefore a need for an improved multiple channel fire sensor system which overcomes the aforementioned problems. In particular, there is a need for an improved fire sensor system which provides adequate discrimination against false triggering signals, while at the same time, which provides for the timely production of a fire suppression command output signal even if radiation obscuring conditions occur which tend to interfere with the proper operation of the system.